Blind fastener with prismatic body

ABSTRACT

A one-piece blind fastener, of the kind which serves as a nut plate, has a head to bear against the exposed face of a structural member having a hole in it, and a prismatic hollow body having preferably four to six flat faces to pass through the hole. The middle part of the body is divided longitudinally into as many strips as it has faces, and its end remote from the head is internally threaded. The bore of the fastener contains a small step or offset so that the major diameter of bore extends from the outer face of the head to the step, and a slightly smaller diameter of bore extends from the step to the threaded portion. When the fastener is shortened by a pull on a threaded draw rod, the longitudinal strips fold outward at the step and bear firmly against the back or blind face of the structure.

United States Patent [191 Allender Mar. 19, 1974 BLIND FASTENER WITH PRISMATIC v BODY Primary Examiner-Edward C. Allen [75] inventor: Meredith L. Allender, Akron, Ohio figg Agent Hargld [73] Assignee: The B. F. Goodrich Company,

New York, NY. a [57] ABSTRACT [22] Filed. July 25, 1972 [21] Appl. No.: 274,852

[52] US. Cl. 85/71 [51] Int. Cl. F16b 13/04 [58] Field of Search... 85/71, 70, 84 56 References Cited UNITED STATES PATENTS 2.255.65Q '9/1941 Burke 85/71 3,174,387" 3/1965 Fischer....

777.134- 12/1904 Palmer..... 2.763.314 9/1956 G111....; .1 3.304.830 2/1967 Shachelford 85/70 I FOREIGN PATENTS 0R APPLICATIONS 9/l9481 Great Britain... 85/71 A one-piece blind fastener, of the kind which serves as a nut plate, has a head to bear against the exposed face of a structural member having a hole in it, and a prismatic hollow body having preferably four to six flat faces to pass through the hole. The middle part of the body is divided longitudinally into as many strips 7 as it has faces, and its end remote from the head is internally threaded. The bore of the fastener contains a 1 small step or offset so that the major diameter of bore 1 10 Claims, 18 Drawing Figures PATENTEUMAR 1 9 @974 3797358 SHEET 1 OF 2 2;: FIG.5

PATENTEBHAR 19 I974 37 73 sum 2 BF 2 FIGJQO 65 63 Flt-3.18 76 1 BLIND FASTENER WITH PRISMATIC BODY" CROSS REFERENCE BACKGROUND This invention relates to blind fasteners, which means fasteners which can be installed entirely from'one side of a structure, and in particular the type having an internal screw thread so that they can be used as nutplates to fasten a separate component of a product to a structure by means of screws. Such blind fasteners are extensively used where it is not convenient or'practical to drill and tap the structure to receive a screw.

Heretofore, one type of blind fastener has generally been cylindrical in shape to form a circular bulge on the back or blind face of the workwhen it is fastened in place, although some similar fasteners have had the external shape of polygonal'prisms with four to six sides, particularly where it is especially important to prevent them from turning in their seat when screws are inserted or removed. In addition, many blind fasteners have been longitudinally slotted so that thestrips between the slots can fold outwardly to pressagainst the back or blind face of the work, and in the prior Shackelford US Pat. application Ser. No. 95,824 such define the location of the folds.

SUMMARY OF THE INVENTION This invention is an integral seamless blind fastener with longitudinal slots so thatit is fastened by outward folding of the metal between the slots to bear against fasteners have had a shallow internal step or offset to I 2 position of the back face of the structureand the portion of smallest internal diameter containing the internal threads.

When such'a fastener is installed by shortening it, by I pulling a threaded draw rod, the strips between the longitudinal slots fold outwardly, withthe fold at the location of the internal step, and are pressed against the back face of the structure. in a tight 180 fold with the tips of the folded strips a substantial distance from the hole in the structure.

Such fasteners have an extremely high resistance to pulling through the holes,'and also maximum resistance to turning in the holes.

DRAWINGS, V

In the accompanying drawings, FIG. 1 is a perspective view of a fastener with a six-sided prismatic body and a cylindrical bore, with slots in the middle of the six faces, FIG. 2 is a longitudinal section and FIG. 3 is a transverse sectionf FIG. 4 shows in perspective the fastener of FIG. 1 after installation in a hole in a structure as seen from the back or blind face,,and FIG. Sis a longitudinal section of the same installation.

FIG. 6 is a perspective view of a six-sided fastener differing from the previous one in having slots at the edges between thesix faces, FIG. 7.is atransverse section and FIG. 8 is a longitudinal section. v

FIG. 9 is a perspectivetview of a four-sided prismatic fastener, FIG. 10 is a longitudinal. section of the fastener, and FIG. 11 is a transverse'sectional view of it.

, FIG. 15 isa view from the head end of a fastener havthe back or blind face of the structure in which it is installed. It is particularly characterized by a noncylindrical or faceted prismatic external shape.

The non-cylindrical shape presents edges which are pressed against the walls of the. hole during setting of the fastener so as to give maximum assurance against turning when a screw is subsequently inserted or removed. This security against turning is especially the case when the fastener is installed in a punched hole of the same size and shape as the body of the fastener rather than. in a circular drilled hole.

In addition, it is essential for best performance and development of maximum strength against pulling out of the hole that specific dimensional relationship be maintained. First, the length of the body between the back of the structure in which the fastener is installed andthe threads in the end mustbe such that the fas tener when installed will presentlong bearing surfaces.

radiating from the fastener, this portion preferably being at least about the same length as the external diameter of the body and may be of a length up to twice its diameter or more. Second, the wall thickness must ing both a prismatic outer surface and a prismatic inner surface so that the part of the hollow body which is to form the folds is of uniform thickness *circumferen tially, and FIG. 16 is a broken longitudinal section of the same fastener.

FIG. 17 is a view from the headend of a fastener having a bore, part of which is prismatic and part of which is cylindrical, and FIG. 18 is a broken longitudinal section of that fastener. I

DETAILED DESCRIPTION Referring to FIGS. 1 to 3, a fastener is shown having a head 20 and a hollow body 21 having the shape of a hexagonal prism of such a size that it will just fit easily through a holein a sheet of metal or the like forming part of a structure. The body 21 has a-longitudinal bore made up of three sectionsof different diameter.

' The end farthest from the head has a bore of smallest diameter 22 and is internally threaded to receive a threaded draw; rod forinstallation, and to receive a screw if'th'e fastener is to be usedas a nut plate.

The central'part of the length has a larger bore 23 which will just permit the draw rod or screw to pass through and enter the internal threads in the far end 22.

on either side of a shallow step 25 or offset in diameter.

In each flat face of the body 21 is a longitudinal narrow slot 26, the length of which is such that it extends at least from about the juncture of the threaded section of bore 22 and the central section of bore 23 at one end to the back face of the structure in which it is installed at the other end. The length just mentioned is the length of the portion of the fastener which folds to grip the back face of the structure in which the fastener is installed, and must be great enough that the strips between the slots will ultimately have a large bearing area on the structure and bear against the structure at a substantial distance from the hole. I

In addition, the step 25, which defines the location of the beginning of the fold in each strip when the fastener is installed, should be about midway between the back face of the structure and the threaded far end, so that the folded strip will project at about a right angle from the axis of the fastener and lie against the back face of the structure. Consequently, the bore 24 at the head end should have a length about equal to that of the central section of bore 23 plus the thickness of the structure plus the thickness of the head.

The fastener is installed by use of conventional tools which are available in a number of designs for manual or power operation, for exertion of a strong pullon a threaded draw rod against the reaction of an anvil engaging the head of the fastener- The fastener is screwed on to the tip of the draw rod, inserted in the hole in the structure, and fastened in place by pulling up the-draw rod to shorten the fastener. The draw rod is then unscrewed to disconnect the tool from the fastener.

The shortening of the fastener causes each of the strips between slots 26 to commence bending outward at the location of the step 25. As the shortening continues, the strips form tight 180 folds and are pressed firmly against the back face of the structure in a flower petal shape as shown in FIGS. 4 and 5, with the folded strips 27 lying against the back face of a structural member 28.

The prismatic shape of the fastener body is found to have a number of unanticipated benefits, in addition to the obvious fact that it provides maximum resistance against turning, particularly when installed in a polygonal hole of the same size and shape as the outside of the fastener body. This can be extremely important, as when used to receive screws fastening automobile seat belts to floor panels. When belts need replacing, after a. year or two of use, it is most helpful to be able to remove the screws without having to grip the fastener, even though the screws may be rusted in place.

An important benefit results from the fact that the thickness of wall of the body of the fastener in the center of each face of the body 21 is considerably less than would be the case if the same amount of metal were used in a cylindrical body. This permits slots 26 to be cut more easily and quickly, because less metal needs to be removed, if the slots are sawed, or a smaller force is required, if the slots are pierced.

Another unanticipated benefit is that the fastener after installation is stiffer and has an increased resistance to pull-through for the same amount of metal, be-

The embodiment shown in FIGS. 6 to 8 has the same external and internal shape as that of FIG. 1. Similarly it has a head 30, body 31, threaded bore 32 at the far end 'of the body, a central section of bore 33 of intermediate diameter anda head end bore 34 of slightly greater diameter separated from bore 33 by a step 35. It differs in that its longitudinal slots 36, instead of being in the middle of the faces, are located at the edges between the several faces. I

This embodiment is somewhat more difficult to manufacture because of the necessity for producing the slots where the metal is thickest, and also at an edge where precise and rigid support of a tool may be required. In other respects it exhibits as good or better properties than that of FIG. 1. y

In particular, in this embodiment the folds are formed in strips having the shape of a shallow channel, with the ends folded toward the channel side. This produces a box-like shape with a maximum of the material at its surfaces to produce the greatest stiffness and resistance to pull-through failures.

The fastener shown in FIGS. 9 to 11 is essentially the same as that of FIG. 1 except that its body has four sides instead of six. It similarly has a head 40, and a body 41 which in this instance has the shape of a square prism. The body at its far end has an internally threaded bore 42 of relatively small diameter, an intermediate section of bore 43 of greater diameter, and a head end bore 44 0f still slightly greater diameter separated from bore 43 by a shallow step 45. Like fastener Like the FIG[ 1, it has a longitudinal slot 46 in each face of the body 41, but since it is a square prism, there are only four slots instead of six.

The fastener of FIG. 9 exhibits all the advantages and benefits of that of FIG. 1, but to a more pronounced extent, because it exhibits a considerably greater difference in wall thickness between the edges of the longitudinal strips formed by slots 46 and the middle zone of the strips.

This fastener is installed exactly like all the other fasteners of this invention, by tension on a threaded draw rod after insertion in a hole of the proper size.

The fastener shown in FIGS. 12 to 14, like that of FIG. 9, has a square body. It has a head 50, a four-sided prismatic body 51 with an internally threaded bore 52 of minimum diameter at the far end of the body, a cen tral section of bore 53 of greater diameter, and a head end bore 54 of still slightly greater diameter separated from central bore 53 by a small step 55. It also has a longitudinal slot 56in the center of each face of the body 51 but of somewhat different shape than the slots 46 of FIG. 9.

In FIG. 9 the slots 46 are shown as extending lengthwise from (but not through) the head 40 to the threaded part of the bore 42, and as being tapered in width with the greatest width outside and smallest width inside. Such slots can be formed, for example, by piercing the walls with longitudinal blades, preferably before drilling or finish reaming of central bore 43 and head end bore 44.

In FIG. 12 the slots 56 are shown with the reverse taper, being of greatest width inside and smallest width outside. Moreover, they extend completely through the head 50. Such slots can be made, for example, by driving a ribbed punch into the fastener from the head end, to gouge or squeeze slots 56 the entire length of the head end bore '54 and central bore 53 but not into threaded bore 52. Such slots extending completely to an end of the fastener( in this case the head end) do not affect the integrity or performance of the fastener as long as a sufficient ring of metal remains at the end to prevent splitting of the end during the installation.

As shown in FIGS. 15 and l6,'it is not essential that the fasteners have a circular bore Thus a slug of metal of the proper size can be headed at one end and can then be partially pierced from the head end by a square pin having a shallow step intermediate its length. Thereafter, the closed end of the body is drilled and tapped, and slots are cut through the head into the remaining part of the length by means of a ribbed punch as described above with respect to FIG. 12.

The resulting fastener, seen from the head end in FIG. 15 and in broken longitudinal section in FIG. 16,

has a head 60 and a square prismatic body 61, the far end of which has a bore of smallest diameter with internal threads 62. A central section has a square bore 63 so thatthe bodyof the fastener in this section has an approximately uniform wall thickness around its circumference. The remainder of the bore 64 extending through the head, is also square but'with a slightly greater dimension so that there is a small step 65 between it and the central section of ,bore 63. Each of the four. faces has a longitudinal slot 66 which in this case extends through the head 60 and the entire length of both square sections of the bore. p

This particular fastener has a strength nearly as great as the form with a circular bore because'the angular shape of the strips at their junction with the threaded far end 62 of the body produces a pronounced stiffness against any further deformation of the installed fastener, and therefore strongly resists bending back of the folded strips toward the far end of the fastener and pulling through the hole.

A still further variation is shown in-FIGS. l7 and 18, in which the fastener has a head 70, and a six-sided prismatic body 71 having an internally threaded far end 72. In this form the central section 73 of the bore has a cylindrical shape, and only the portion of the bore 74 at the head end has a six-sided prismatic shape like that of the outside of body 71. Also in this form the dimension from one internal face of the prismatic bore 74 to the opposite face does not need to be greater than the diameter of the central cylindrical section 73 of the bore. The step 75 forming the transition between the central section 73 of the bore and the head end bore 74 consequently exists principally in the corners of the head end bore 74. This form accordingly provides a lateral support of a screw inserted in the installed fastener, against lateral displacement or shear' deformation, without requiring use of a non-standard screw having its threaded tip of a smaller diameter than the remainder of its shank. Finally, this form, like all the others, has a longitudinal slot 76 in each face of the prismatic body 71, for installation in the same manner as all the other forms of the invention described herein, and for folding of the. resulting strips against the back face of the structure, for maximum strength against pull through the hole in the structure.

Manifestly, many minor variations in structure arev possible without departing from the scope of the invention. Thus the shape of the head may be modified to suit variousparticular needs, such as the conical shape of a flat head to fit a conically countersunk hole.

1 section.

It is not essential that the fastener body be of exactly can be varied, with any of the forms whether shown as having four or six faces having a different number of faces. However numbers smaller than four or greater than six are ,not presently preferred.

1. A one-piece blind fastener comprising a head and a prism shaped body integral with the head, the fastener having a longitudinal bore extending through the head and the body and having three sections, the bore of the section farthest from the head being of smallest diameter and being internally threaded, the bore of the central section being of a greaterdiameter to clear the tips of threads of a screwfitting the internal threads the boreof the other section being of slightly greater maximum diameterand slightly smaller wall thickness along its length than the central section, in at least several circumferential locations,-with an abrupt internal shallow step or offset between it and the central section in the same circumferential locations, the last mentioned section extending from the step to and through the head, the portion of the body capable of passing completely through a hole in a structure in which it is to be installed but not including the internally threaded section farthest from the head being of essentially uniform external size and shape and of a length at least approximately as great as its maximum external diameter, and longitudinal slots in the said portion dividing it into strips.

2. A fastener as in claim 1, in which the numbers of slots is the same as the number of faces of the prismatic body. I I

3. A fastener as in claim 2, in which the longitudinal slots are in the centerof the faces. 7 i

4. A fastener as in claim 1 in which the prismatic body has notless than four nor more than six faces.

' 5. A fastener as in claim I, in which the prismatic body has four faces.

6. A fastener as in claim 1, in which each section of the bore other than the threaded section is cylindrical.

7. A fastener as in claim 1, in which the section of the bore from the step to the headis prism shaped and the wall of the body in that section has an approximately uniform thickness.

8. A fastener as in claim 7, in which the central section of the bore, from the internally threaded end to the step, iscyliridrical.

- 9. A fastener as in claim 1, in which the step is approximately midway between the location of the back face of the structure and the internally threaded end 10. A fastener as in claim 7, in which the prismatic body has six faces, the longitudinal slots are in the centers of the faces, and the step is approximately midway,

between the location of the back face of the structure 

1. A one-piece blind fastener comprising a head and a prism shaped body integral with the head, the fastener having a longitudinal bore extending through the head and the body and having three sections, the bore of the section farthest from the head being of smallest diameter and being internally threaded, the bore of the central section being of a greater diameter to clear the tips of threads of a screw fitting the internal threads, the bore of the other section being of slightly greater maximum diameter and slightly smaller wall thickness along its length than the central section, in at least several circumferential locations, with an abrupt internal shallow step or offset between it and the central section in the same circumferential locations, the last mentioned section extending from the step to aNd through the head, the portion of the body capable of passing completely through a hole in a structure in which it is to be installed but not including the internally threaded section farthest from the head being of essentially uniform external size and shape and of a length at least approximately as great as its maximum external diameter, and longitudinal slots in the said portion dividing it into strips.
 2. A fastener as in claim 1, in which the numbers of slots is the same as the number of faces of the prismatic body.
 3. A fastener as in claim 2, in which the longitudinal slots are in the center of the faces.
 4. A fastener as in claim 1, in which the prismatic body has not less than four nor more than six faces.
 5. A fastener as in claim 1, in which the prismatic body has four faces.
 6. A fastener as in claim 1, in which each section of the bore other than the threaded section is cylindrical.
 7. A fastener as in claim 1, in which the section of the bore from the step to the head is prism shaped and the wall of the body in that section has an approximately uniform thickness.
 8. A fastener as in claim 7, in which the central section of the bore, from the internally threaded end to the step, is cylindrical.
 9. A fastener as in claim 1, in which the step is approximately midway between the location of the back face of the structure and the internally threaded end section.
 10. A fastener as in claim 7, in which the prismatic body has six faces, the longitudinal slots are in the centers of the faces, and the step is approximately midway between the location of the back face of the structure and the internally threaded end section. 